Hi chandleryang,
first of all i’d suggest you to use the “print screen” button to take screenshots, instead of photographing your screen with external devices.
It’ll store the snapshot to the clipboard and you can paste it in any picture editing app you want, even MS Paint will work.
As for your issue, I guess you have used a Lathe-Object or something like that to create the shape.
After converting the generator to an editable polygon object, make sure that the face normals of all polygons are facing in the right direction.
In polygon mode, select>select all.
Orange tint means it’s the front of the face, blue tint means backside.
It’s possible to use the align normals and flip normals commands to fix the orientation of the face normals.
You want all of them facing you with their frontside outwards ofc.
In most realtime engines, the backface is culled by default, which means it doesn’t render.
(you can have that in Cinema too by enabling/disabling the culling in the Viewport options>backface culling)
There is a Material option too, that enables the rendering of backfaces on a mesh, but this should only be used if it’s really neccessary.